The subject matter disclosed herein relates to a three-dimensional coordinate scanner and in particular to a triangulation-type scanner having multiple modalities of data acquisition.
The acquisition of three-dimensional coordinates of an object or an environment is known. Various techniques may be used, such as time-of-flight or triangulation methods for example. A time-of-flight systems such as a laser tracker, total station, or time-of-flight scanner may direct a beam of light such as a laser beam toward a retroreflector target or a spot on the surface of the object. An absolute distance meter is used to determine the distance to the target or spot based on length of time it takes the light to travel to the target or spot and return. By moving the laser beam or the target over the surface of the object, the coordinates of the object may be ascertained. Time-of-flight systems have advantages in having relatively high accuracy, but in some cases may be slower than some other systems since time-of-flight systems must usually measure each point on the surface individually.
In contrast, a scanner that uses triangulation to measure three-dimensional coordinates projects onto a surface either a pattern of light in a line (e.g. a laser line from a laser line probe) or a pattern of light covering an area (e.g. structured light) onto the surface. A camera is coupled to the projector in a fixed relationship, for example, by attaching the camera and the projector to a common frame. The light emitted from the projector is reflected off of the surface and detected by the camera. Since the camera and projector are arranged in a fixed relationship, the distance to the object may be determined using trigonometric principles. Compared to coordinate measurement devices that use tactile probes, triangulation systems provide advantages in quickly acquiring coordinate data over a large area. In this document, the resulting collection of three-dimensional coordinate values provided by the triangulation system is referred to as point cloud data or simply a point cloud.
A number of issues may interfere with the acquisition of high accuracy point cloud data when using a laser scanner. These may arise during scanning include but are not limited to: variations in the level of light received over the camera image plane as a result of variations in reflectance of the object surface or variations in the angle of incidence of the surface relative to the projected light; low resolution near edges such as the edges of holes; and multipath interference for example. In some cases, the operator may be unaware of or unable to eliminate these scanning anomalies. In these cases, missing or faulty point cloud data is the result.
Accordingly, while existing scanners are suitable for their intended purpose the need for improvement remains, particularly in providing a scanner that can adapt to undesirable conditions and provide improved data point acquisition.